1. Field of the Invention
The present invention relates to a recording apparatus configured to eject ink drops from ink ejection ports provided in recording heads on the basis of recording data to record an image on a recording medium.
2. Description of the Related Art
An ink jet recording apparatus generally includes a recording head in which ink ejection ports and recording elements serving as energy generators including heaters and piezoelectric elements and adapted to eject ink drops are arranged in correspondence with each other. The recording head is moved in a main scanning direction and ink drops are ejected in a recording area to perform recording scanning. A recording medium is fed in a sub-scanning direction perpendicular to the main scanning direction. The recording scanning and the feeding of the recording medium are repeatedly performed to record an image on the recording medium.
Due to a reason such as the high cost of power supply, it may be difficult to provide a large power supply capacity sufficient for an ink jet recording apparatus to simultaneously eject ink drops from all ink ejection ports in each array of ink ejection ports (array of recording elements) of the recording head. In order to overcome this problem, the recording elements are driven in a time-division manner. The time-division driving will now be described. For each array of ink ejection ports, the recording elements are divided into a plurality of groups, and the recording elements in each of the groups are assigned different blocks. The recording elements belonging to the same block are driven simultaneously or substantially simultaneously, and the recording elements in the respective blocks are sequentially driven at certain intervals of time. The driving of the recording elements is performed through one cycle, thereby driving all the recording elements. This driving operation is repeated in the main scanning direction to perform recording in a recording area corresponding to one line of main scanning.
In an ink jet recording apparatus, an error in attachment of a recording head or error in assembling of the recording head may cause the recording head to be inclined when it is attached to the ink jet recording apparatus. Thus, deviation in position of dots formed in accordance with this inclination, called inclination deviation, may occur.
The inclination deviation will be described in detail with reference to FIGS. 30 and 31.
FIG. 30 shows an arrangement of dots formed on a recording medium in a case where a recording head is ideally attached to an ink jet recording apparatus, that is, in a case where no inclination deviation has occurred. In FIG. 30, a recording head 11 is attached parallel to a sub-scanning direction indicated by an arrow B, and is moved from left to right in a main scanning direction indicated by an arrow A across the recording medium 12. The recording medium 12 is fed upward from below, as viewed in FIG. 30, in the direction indicated by the arrow B. The top side of FIG. 30 is a downstream side in the sub-scanning direction, and the bottom side of FIG. 30 is an upstream side in the sub-scanning direction.
Recording elements (not shown) disposed in correspondence with 128 ink ejection ports 13 of the recording head 11 are divided into eight groups (group 0 to group 7) each having 16 recording elements. The recording elements in each of the groups are assigned different blocks, and are sequentially driven at certain intervals of time in units of recording elements in the same block. In this example, the recording elements are divided, in turn, into groups 0 to 7 each having 16 recording elements from the downstream side in the sub-scanning direction. The recording elements in each of the groups are assigned blocks 0 to 15, in order, from the downstream side in the sub-scanning direction. The recording elements in each of the groups are driven in the order of block 0, block 1, block 2, . . . , and block 15, and one cycle of driving is thus completed.
Without inclination deviation, dots formed by one cycle of driving of the recording elements of blocks 0 to 15 are formed within the same column (region with a width of one pixel). FIG. 30 shows an arrangement of dots formed on the recording medium 12 by driving the recording elements in the order of blocks 0 to 15 and assigning recording data for three columns, namely, the first to third columns, to the recording elements. In this way, dots formed by one cycle of driving of recording elements in each group are arranged in the same column, thereby obtaining an image having a high recording quality.
FIG. 31 shows an arrangement of dots as a result of the occurrence of inclination deviation when an image is recorded with a structure similar to that shown in FIG. 30. As shown in FIG. 31, dots formed by the recording elements that are assigned to the same block are shifted in the main scanning direction between the upstream side and the downstream side. Further, some dots may be formed at positions that lie outside the target column where the dots are to be arranged. For example, for group 2, four dots of blocks 0 to 3 are formed outside the target column. Due to the occurrence of such inclination deviation, dots may be formed at positions outside the target column, leading to deterioration in image quality.
A technique has been proposed for correcting inclination deviation by providing a detector configured to detect information regarding inclination deviation and changing ejection timings of a recording head on the basis of the detected information regarding inclination deviation.
Japanese Patent Laid-Open No. 2004-09489 describes an ink jet recording apparatus arranged to record an image by time-division driving, in which the position at which recording data is read from a recording buffer is changed in accordance with inclination deviation to change ejection timings of a recording head.
An inclination deviation correction method described in Japanese Patent Laid-Open No. 2004-09489 will be described with reference to FIGS. 32 and 33.
The ink jet recording apparatus described in Japanese Patent Laid-Open No. 2004-09489 has a structure similar to that shown in FIG. 30. That is, recording elements provided in a recording head 11 are divided into eight groups 0 to 7, each having 16 recording elements, and the recording elements in each of the groups are assigned block numbers 0 to 15. The recording elements in each of the groups are driven in the order of block 0, block 1, block 2, . . . , and block 15. The following description will be given in the context of an example in which all ink ejection ports 13 of the recording head 11 are used to form dots in an area of three columns from the first to third columns to record an image.
In this example, the recording head 11 is inclined clockwise when it is attached to a recording medium 12, thus causing inclination deviation in which positions of dots formed by the ink ejection ports 13 located at both ends of the recording head 11 are about one column shifted in the main scanning direction.
FIG. 32 is a diagram showing nozzle numbers assigned to the recording elements of groups 0 to 7, a driving order, recording data, and a dot arrangement. The dot arrangement shown in FIG. 32 represents a schematic arrangement of dots formed on the recording medium 12 under the absence of inclination deviation. The nozzle numbers are numbers that are provisionally assigned to the individual recording elements, and the recording elements are assigned nozzle numbers 0 to 127 in order from the recording element located downstream in the sub-scanning direction.
In Japanese Patent Laid-Open No. 2004-09489, the position at which recording data is read from a recording buffer is changed for every group in accordance with inclination deviation. In case of one-column inclination deviation, as shown in FIG. 32, recording data assigned to the recording elements of groups 4 to 7 is read from a position one column shifted in the main scanning direction with respect to the true column.
Specifically, recording data is assigned to the recording elements of groups 0 to 3 so that dots are formed in an area of the first to third columns. The recording elements of groups 4 to 7 are, on the other hand, assigned recording data by changing the read position of the recording data so that dots are formed in an area of the second to fourth columns.
FIG. 33 shows an actual arrangement of dots formed on a recording medium as a result of changing the read position of recording data in the manner described with reference to FIG. 32. In FIG. 33, hollow circles shown on the recording medium 12 in correspondence with groups 4 to 7 represent dots that will be formed when recording data of the first column is assigned to the recording elements of groups 4 to 7 without performing the above-described correction. As a result of the correction of inclination deviation described in Japanese Patent Laid-Open No. 2004-09489, the dots for groups 4 to 7 are formed at positions one column offset to the right in the main scanning direction with respect to the positions indicated by the hollow circles. Thus, as is apparent from FIG. 33, the amount of deviation in the main scanning direction for dots in the same block can be reduced between the upstream and downstream sides in the sub-scanning direction.
In the correction method described in Japanese Patent Laid-Open No. 2004-09489, however, other problems may occur. In this method, the read position of recording data is changed for all recording elements within a group. Thus, for a group for which the read position of recording data has been changed, a dot that lies outside the true column may exist. For example, focusing on the first column of group 6, without correction of inclination deviation, four dots for blocks 12 to 15 are arranged in the first column and the rest 12 dots for blocks 0 to 11 are arranged to the left with respect to the first column. If, as a result of the correction of inclination deviation, recording data for the first column is assigned at a timing at which all the recording elements within the group are recorded in the second column, the four dots for blocks 12 to 15 are arranged in the second column instead of the true, first column.
Moreover, depending on the amount of inclination of the recording head, like groups 1 to 3, a group may exist for which even a dot arranged at a position outside the true column might not be corrected.
The correction method described in Japanese Patent Laid-Open No. 2004-09489 can reduce deterioration in image quality caused by inclination deviation. However, a dot may be arranged at a position outside the correct area. Furthermore, if the amount of inclination of the recording head is small, a group for which correction is not performed may exist and a dot outside the true column may not be corrected. In such an existing method of correcting inclination deviation, therefore, there is a limit to the degree of preventing deterioration in image quality.